Colloidal behavior of aqueous montmorillonite suspensions in the presence of non-ionic polymer

In this paper we characterized at first, the rheological behavior of the bentonite suspensions and the aqueous solutions of polyethylene oxide (PEO), then we were investigated the influence of this polymer in a water-based drilling fluid model (6% of bentonite suspension). The objective is to exhibit how the non ionic polymer with molecular weight 6×103 g/mol. of varying concentration mass (0.7%, 1%, 2% et 3%) significantly alter the rheological properties (yield stress, viscosity, loss and elastic modulus) of the bentonite suspensions. The rheological measurements made in simple shear and in dynamic on the mixture (water-bentonite-PEO), showed rheological properties of bentonite suspensions both in the presence and absence of non-ionic polymer. The PEO presents an affinity for the bentonite particles slowing down their kinetic aggregation. The analysis by X-rays diffraction also allowed understanding the structure of this mixture. It had revealed the intercalation between of the clay platelets on one hand, and the links bridges assured by the chains of polymer between bentonite particles beyond a critical concentration in PEO on the other hand. The Herschel- Bulkley rheological model is used for the correlation of our experimental result

Numerical Simulation of the Mechanical Response of the Tunnels in the Saturated Soils by Plaxis

The forecast of settlement and movements caused by tunneling represents a significant challenge of technology. The evaluation of these movements is indeed of primary importance in order to prevent them. The methods of calculation making it possible to evaluate displacements and deformations in the ground due to tunneling give only one approximation of the true amplitudes of the movements in the ground. It is one of the assets of the Finite Element Method (FEM) which makes it possible a priori to treat configurations more complex and closer to reality. Our objective in this study is to calculate numerically the various movements caused by the construction of a shallow tunnel using a shield using PLAXIS 2D, the behavior of the ground is described by a perfectly plastic elastic model based on the criterion of Mohr-Coulomb. A comparison between the various methods: empirical, analytical and numerical in terms of settlement on the surface was carried out. The validation of these results was made by using results drawn from literature. We have also carried out a parametric study in order to analyze the influence of various geometrical and geotechnical parameters on the behavior of grounds due to tunneling. Lastly, we have treated the same example by supposing the existence of structures near the tunnel in order to see the influence of the presence of other structures on the profile of the settlements caused by tunneling. Results of our work agreed with those in literature

Study of Bryophytic Flora in the Ramsar Wetland of Merja Zerga (North-west of Morocco)

The research undertaken in the IBA and Ramsar wetland of Merja Zerga at Moulay Bousselham were interested only in the higher plants. Our study tends then to contribute to enrich the knowledge about the bryophytic flora of this area by filling the gaps in this field. Thus, we carried out a systematic sampling with a stop and a harvest in each encountered bryophyte population. This prospection enabled us to find 26 species of bryophytes including 22 species of mosses belonging to 15 genera and 9 families, and 4 species of liverworts belonging to 3 genera and 3 families. The relative low specificity of this wetland can be explained by the influence of sea spray and the strong anthropic disturbance. A comparison with previous studies allowed us to conclude that 11 species were observed for the first time in the area

Study of the bryological flora at the archaeological site of Chellah, Morocco

The Chellah archaeological site in Rabat, listed as a cultural asset since 2012 on UNESCO's World Heritage List, is subject to significant biodeterioration. The aim of this study is to identify the bryophytes that have an important impact on the destruction of the substrate. For this purpose, three prospectionswere carried out in autumn 2014, spring 2015 and winter 2016. The systematic sampling carried out allowed us to identify 20 species of bryophytes belonging to 10 botanical families, of which 4are dominant with 13 species equivalent to 65% of the total. The four families are Pottiaceae, Brachyceciaceae, Funariaceae and Bryaceae; they belong to the class of Muscinae. The liverworts are represented by only 6 species, representing 30% of the total population. Among the 20 species inventoried, 3 are newly observed in the region of Rabat: Entosthodon pulchellus (H. Philib.) Brugués; Dydimodon Fallax Hedw. and Trichostomum crispulum Bruch. When bryophytes settle on substrates, a preliminary soilis initiated to the detriment of the quality of materials and their durability

Pathogenicity of Helminthosporium rostrata on rice varieties widely grown in Morocco

The plants of rice varieties (Arco, Thaibonnet and Elio) were inoculated with three isolates of Helminthosporium rostrata (HR1 HR2 and HR3), isolated for the first time in Morocco from the rice seed of Taibonnet variety at the end of the growing season. The results obtained showed that all the isolates are able to induce the disease on rice plants and sporulate on the foliar lesions. HR1, HR2 and HR3 was respectively the most pathogenic on Elio (I.C = 113), Arco (I.C = 212.5), and Taibonnet (130.48). The symptoms induced by the isolates are similar to those induced by Helminthosporium sativum on rice